Conventional radiographic examination rooms include a radiographic table and/or radiographic wallstand. The radiographic table and/or radiographic wallstand each contain an image receptor. Medical imaging equipment such as an X-ray source and the collimator is mounted to an overhead tube support (OTS) in the vicinity of the radiographic table and/or the radiographic wallstand for performing diagnostic imaging procedures. The X-ray source and the collimator comprise a tube mount assembly.
The tube mount assembly is aligned with the receptor for imaging of a subject. To align the tube mount assembly with a receptor, the tube mount assembly and OTS move in three linear motions (lateral, longitudinal, vertical) which are perpendicular to each other, and the tube mount assembly moves in two rotational rotations (rotation about the vertical axis, and rotation about one horizontal axis), for a total of five axes.
Manual positioning of the X-ray source, collimator and OTS is performed by an operator releasing locks on each of the five axes, moving the tube mount assembly to a position of alignment with a receptor, the position being indicated by a “detent,” and stopping the tube mount assembly at that position for each of the five axes. The detent is a means of indicating to the operator that the OTS has reached an aligned position along an axis, either by mechanical sensation, of a wheel dropping into a groove, or of an electromechanical lock engaging, or of a visual indication.
Because alignment of the tube mount assembly with a receptor has been mandated by US Federal law, (DHHS CFR21 Subchapter J), many different techniques have been developed to determine proper alignment, and to secure the tube mount assembly in a properly aligned position. In some techniques the operator presses a manual release for a tooth-and-slot lock, and moves the axis until the tube mount assembly reaches the proper position at which the tooth is engaged in another slot. In other implementations, the operator presses a button, which releases an electromechanical friction lock, and when the proper position is reached, the electromechanical friction lock is again engaged. In some other implementations, the “detent” is created by a roller on a smooth surface engaging a transverse slot, creating a tactile perception to the operator that the proper position has been reached.
What is common to all of these techniques is that at least one detent is at a fixed position along an axis of motion at a position in which the tube mount assembly is aligned with a receptor. The operator seeks a detent position by releasing some holding means, or overcoming friction, in order to move the tube mount assembly along that axis to the detent position. When the detent position is reached an indicator will indicate that the detent position has been reached. The indication is a tactile sensation, an audible tone, and/or a visual indication such as a light, etc. Once the operator releases control of that axis of motion, further motion past the detent position is prevented, either by friction, by spring pressure on a wheel in a slot, and/or by engagement of a tooth in a slot, or by some other means. While detent positions may be different for a radiographic table receptor than for a radiographic wallstand image receptor, for each receptor, they are fixed positions of the axes.
One limitation of conventional systems is that the positions of the detents are relative to the axes of motion of the OTS. As a result of the relativity of the positions, it is necessary to align the receptors of the radiographic table and radiographic wallstand parallel or perpendicular to the linear axes of motion of the OTS. To understand this, consider the two examples below:
EXAMPLE A: In one example, there is a lateral detent for the table, which is a fixed position across the width of the table, which aligns with the center of the image receptor.
The image receptor is provided means to move along the length of the table, and (in one embodiment) has a motorized drive, which tracks the position of the X-ray tube and collimator attached to the OTS. So it is possible to position the OTS in the lateral detent, and manually move the OTS along the table, maintaining alignment with the receptor. This alignment is maintained because the lateral position of the OTS is locked at a specific location along the lateral positioning rails, and the longitudinal position of the receptor tracks the longitudinal position of the OTS as it moves along the longitudinal positioning rails.
The detent position is a fixed location of the OTS on the lateral positioning rails.
However, it can be clearly seen that the lateral detent achieved by this means is only as accurate as the alignment of the longitudinal direction of the table with the longitudinal direction of motion of the OTS in the longitudinal positioning rails.
An additional detent position is provided by a fixed mechanical stop to maintain the rotational position of the OTS about the vertical rotational axis, so that the rotational position of the X-ray field about the center of the image field is correct.
An additional detent is provided to maintain the proper vertical separation between the X-ray tube focal spot and the receptor.
An additional detent may be provided for the rotational position of the horizontal rotational axis, (either a hard stop, or a user perceptible position) and/or the longitudinal motion of the receptor may be adjusted to correctly position the receptor if the horizontal axis of the OTS is rotated.
This requires the alignment of the table to the positioning rails of the OTS, as stated earlier.
EXAMPLE B: In another example, a detent position provides alignment of the X-ray tube and the collimator to the horizontal center of the radiographic wallstand image receptor, when the radiographic wallstand receptor is in the vertical position.
When the OTS is moved manually nearer or farther away from the radiographic wallstand, it is required that the focal spot of the X-ray source assembly remain the centerline extending from the image receptor perpendicular to the image plane.
This is accomplished by placing the image plane perpendicular to either the lateral or longitudinal positioning rails.
The X-ray tube and collimator is placed in the proper position relative to the radiographic wallstand as follows:
The horizontal rotational axis is rotated so that the central ray of the X-ray field is in the horizontal plane. A detent is provided for this position.
The vertical rotation axis is rotated so that the central ray lies along either the lateral positioning rails, or the longitudinal positioning rails, whichever is perpendicular to the image plane. A detent or lock of some sort is provided for this position.
The OTS is moved along the lateral or longitudinal positioning rails (whichever is parallel to the image plane) until the central ray of the X-ray field is at the horizontal center of the image receptor. A detent is provided for this position, as a fixed position (within a tolerance) in the relevant horizontal motion axis.
The vertical extension of the OTS is adjusted so that the central ray of the X-ray field is at the vertical center of the image receptor. A detent is provided for this position, as a fixed position (within a tolerance) in the vertical motion axis.
The distance from the X-ray source to the image receptor may now be varied by moving along the remaining set of positioning rails, and the image will remain properly centered.
Note that the sequence above is arbitrary, and in fact other variations exist, such as automatic positioning of the OTS to match the vertical position of the radiographic wallstand image receptor. In addition, note that the receptor for the radiographic wallstand can be rotated over a range of angles, for example, from −20 to +90 degrees, relative to the vertical position.
However, in the two examples above, it can be seen that it is necessary for the table and radiographic wallstand to be aligned at zero or 90 degrees relative to the lateral and/or longitudinal positioning rails of the OTS, and the accuracy with which the manual motions described will “track” the image receptor is determined by the accuracy of this alignment. This limits the flexibility of room configurations, and at the same time, limits the accuracy of positioning.
Manual positioning in conventional systems requires releasing one or more locks for the axes of the OTS, typically using switches mounted on the user interface, or on the collimator, and pushing the tube mount assembly in the desired direction of motion. Motion is prevented in those directions for which the locks or detents are not released in this manner. It should be noted that the tube mount assembly may be locked in any position of the translation motions, and not only in the detent position.
Additionally, in conventional systems, the radiographic wallstand image receptor is typically mounted to the floor or wall, and the X-ray tube suspension is typically mounted to the ceiling. As a result of this, the motion of each is not necessarily perfectly vertical, as there may be some leaning of the radiographic wallstand, and the extending column of the OTS may not produce perfectly vertical motion. Additionally, both devices may bow or distort due to the influence of gravity, as they are not perfectly rigid.
As a consequence of bowing or distortion, the alignment of a focal spot of the X-ray tube is only accurately aligned for one particular height of the radiographic wallstand image receptor, and thus is likely to be misaligned at other heights.
Additionally, in conventional systems, the lock release switches on the UIF or the collimator control specific locks, and this causes some confusion for the operator, because if the X-ray tube and collimator are rotated 90 degrees about the vertical rotation axis of the OTS, the operator must remember that the function of the switches is now reversed, in that the motion of the OTS relative to the operator has not rotated. Also, at intermediate angles, the motion allowed is at skewed angles, relative to the operator. A more intuitive way of manually moving the OTS would improve usability of the tube mount assembly.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art to increase the extent of flexibility of room configurations and improve the accuracy of positioning of the apparatus. There is also a need to maintain proper alignment over the full range of travel of the radiographic wallstand image receptor. There is a further need in the art for an ability to correct for imperfections in geometry in the apparatus and to allow for greater tolerance in precision in manufacturing and installation. This is an additional need in the art to reduce confusion of the operator in the relationship between the function of the switches and the motion of the OTS. There is also a need for a system that accommodates an image receptor of a wallstand or a table positioned at an angle other than 0 or 90 degrees to a positioning rails.